The pressurizer permits the maintenance of the pressure in the primary circuit between certain specified limits, either by aspersion, when the pressure has a tendency to exceed the accepted upper limit, or by electrical heating of the primary fluid, when the pressure has a tendency to fall below the accepted lower limit. These operations are effected within the pressurizer which comprises, in particular, a casing having a domed base through which electrical heating rods are introduced into the pressurizer.
Passage collars are fixed by welding on the base of the pressurizer, each at the location of a passage opening. The heating rods are introduced into the collars and welded at their ends, in such a manner as to ensure mechanical retention and the sealing of the connection.
The heating rods are constructed in the form of glove fingers enclosing the heating resistors and comprising an open end at the location of the outer end of the passage collar, in order to ensure the connection and the supply of the electrical resistors.
Certain heating rods may become defective in service, so that it is necessary to check periodically their good state of operation.
In the case where the presence of a defective rod has been detected, the replacement thereof is carried out in such a manner as to continue to ensure a satisfactory operation of the pressurizer.
In a general way, the replacement of a heating rod of a pressurizer is carried out by a sequence of successive operations comprising, in particular, sectioning of the collar, extraction of the defective rod, cleaning and machining of the cut-off end of the collar, positioning of a replacement rod, temporary fixing of this rod on the collar by welding points, and final fixing of the rod by formation of a continuous circular weld ensuring the junction between the rod and the end of the collar. Various monitoring operations must be carried out between the operational phases set forth hereinabove.
The welding operations are carried out by the TIG process, the continuous welding band between the rod and the collar being constructed in a plurality of passes, by an automatic machine ensuring the fusion of a fusible metal wire.
Such an automatic TIG welding installation with fusible metal is extremely bulky and difficult to utilize to construct the junction, by welding, of tubular parts of small diameter, such as a heating rod and a passage collar of a pressurizer.